Production of hybrid 16-membered macrolides by expressing combinations of polyketide synthase genes in engineered Streptomyces fradiae hosts

Combinations of the five polyketide synthase (PKS) genes for biosynthesis of tylosin in Streptomyces fradiae (tylG), spiramycin in Streptomyces ambofaciens (srmG), or chalcomycin in Streptomyces bikiniensis (chmG) were expressed in engineered hosts derived from a tylosin-producing strain of S. fradiae. Surprisingly efficient synthesis of compounds predicted from the expressed hybrid PKS was obtained. The post-PKS tailoring enzymes of tylosin biosynthesis acted efficiently on the hybrid intermediates with the exception of TylH-catalyzed hydroxylation of the methyl group at C14, which was efficient if C4 bore a methyl group, but inefficient if a methoxyl was present. Moreover, for some compounds, oxidation of the C6 ethyl side chain to an unprecedented carboxylic acid was observed. By also expressing chmH, a homolog of tylH from the chalcomycin gene cluster, efficient hydroxylation of the 14-methyl group was restored.     

Anomalous fluorescence properties of 4-N,N-dimethylaminobenzoic acid in polar solvents

4-N,N-Dimethylaminobenzoic acid exhibits anomalous fluorescence in polar and hydrogen-bonding solvents. The fluorescence spectra and kinetics suggest that this arises due to the formation of a ground-state dimer or higher polymer. Preliminary measurements in hexane containing small amounts of polar acetonitrile do not rule out the possibility of exciplex formation also occurring.     

Functional expression of genes involved in the biosynthesis of the novel polyketide chain extension unit, methoxymalonyl-acyl carrier protein, and engineered biosynthesis of 2-desmethyl-2-methoxy-6-deoxyerythronolide B

A subcluster of five genes, asm13-17, from the ansamitocin biosynthetic gene cluster of Actinosynnema pretiosum was coexpressed in Streptomyces lividans with the genes encoding the 6-deoxyerythronolide B (6-DEB) synthase from Saccharopolyspora erythraea, in which the methylmalonate-specifying AT6 domain had been replaced by the methoxymalonate-specifying AT8 domain from the FK520 cluster of Streptomyces hygroscopicus. The engineered strain produced the predicted product, 2-desmethyl-2-methoxy-DEB, instead of 6-DEB and 2-desmethyl-6-DEB, which were formed in the absence of the asm13-17 cassette, indicating that asm13-17 are sufficient for synthesis of this unusual chain extension unit. Deletion of asm17, encoding a methyltransferase, from the cassette gave 6-DEB instead of its hydroxy analogue, indicating that methylation of the extender unit is required for its incorporation.     

Creatine kinase B deficient neurons exhibit an increased fraction of motile mitochondria

Background  

Neurons require an elaborate system of intracellular transport to distribute cargo throughout axonal and dendritic projections. Active anterograde and retrograde transport of mitochondria serves in local energy distribution, but at the same time also requires input of ATP. Here we studied whether brain-type creatine kinase (CK-B), a key enzyme for high-energy phosphoryl transfer between ATP and CrP in brain, has an intermediary role in the reciprocal coordination between mitochondrial motility and energy distribution. Therefore, we analysed the impact of brain-type creatine kinase (CK-B) deficiency on transport activity and velocity of mitochondria in primary murine neurons and made a comparison to the fate of amyloid precursor protein (APP) cargo in these cells, using live cell imaging.     

Genetic Engineering of Streptomyces coelicolor A3(2) for the Enantioselective Reduction of Unnatural beta-Keto-Ester Substrates

Potential "reagents" for the enantioselective reduction, and other biotransformations, of beta-keto-esters result from the genetic engineering of Streptomyces coelicolor A3(2). For example, incubation of the N-acetylcysteamine thioester 1 with the recombinant strain CH999/pIJ5675 followed by treatment with MeOH/HCl gave the lactone 2 as essentially a single enantiomer.